The invention relates to an optical signal receiving circuit used in an optical signal communication and a method for receiving the optical signal.
A primitive optical signal receiving circuit is composed of a photodiode and a simple pre-amplifier of a resistance feed back type. However, in this receiving circuit, the pre-amplifier is saturated in case that an optical signal with a high level is applied to the photodiode, and the optical signal cannot be normally regenerated and a dynamic range cannot be secured.
A conventional optical signal receiving circuit of other type comprises two receiving circuits with different gains, one of which is selected in accordance with the input optical signal level. However, it is difficult to design a selecting circuit for the two receiving circuits, especially in case that the optical signal of a high frequency is received. Moreover, the optical receiving circuit of this type is high-priced as compared with that constituted of single receiving circuit.
Earnest efforts have been made to develop an optical signal receiving circuit, which is constituted of a single receiving circuit and secures a dynamic range. However, it is common to the most of these optical receiving circuits that the pre-amplifier is controlled by means of a feed back circuit. In case that the feed back circuit is used in the amplifier, the feed back circuit is apt to be a cause for oscillation of the amplifier, and particular attention must be paid to the design of the feed back circuit.
Accordingly, it is an object of the invention to provide an optical signal receiving circuit, which has a low noise characteristic, secures a dynamic range, and is simply designed and low priced.
It is a further object of the invention to provide method for receiving an optical signal, which has a low noise characteristic, secures a dynamic range, and is simple designed and low priced.
According to the first feature of the invention, an optical receiving signal circuit comprises:
a photodiode for converting an input optical signal into a current signal,
a current feed back amplifier for converting the current signal supplied from a cathode of the photodiode into a voltage signal,
wherein input and output terminals of the current feed back amplifier are connected by a first resistor,
a second resistor inserted between a cathode of the photodiode and a terminal of a power supply for a reverse bias voltage,
wherein the reverse bias voltage of the cathode of the photodiode is supplied through the second resistor,
a peak-detecting circuit for detecting an amplitude of a receiving signal voltage generated by the current signal between both ends of the second resistor, and
an adjusting circuit for controlling a feed back current of the current feed back amplifier based on an output voltage of the peak-detecting circuit.
According to the second feature of the invention, a method for receiving an optical signal, in which a photodiode for converting an optical signal into a current signal and a current feed back amplifier having input and output terminals connected by a first resistor for converting the current signal supplied from a cathode of the photodiode into a voltage signal are used, comprises the steps of:
detecting an output current of the photodiode,
controlling a feed back current of the current feed back amplifier in accordance with the output current of the photodiode so that the feed back current of the current feed back amplifier is decreased in case that the output current of the photodiode increases and the feed back current of the current feed back amplifier is increased in case that the output current of the photodiode decreases, and
stabilizing the output current of the photodiode.